There are many hinge designs used in orthopaedic splints and braces, most of them having either a single pivot or two pivots supporting arms which are geared together. Bipivotal hinges in which the arms are not geared together but are truly independently pivotal about their respective axes have become increasingly popular in recent years with the realization that such a construction is superior to the others in providing the freedom necessary to accommodate the complex and changing locus of the axis of the knee during the full flexion/extension cycle.
We have developed a number of adjustment mechanisms for true bipivotal hinges, all of them providing continuously variable stops, and these are described in GB 2,182,714, published UK application 2,208,065A, and in European patent publication 0,109,847. However, the degree of sophistication disclosed therein may add substantially to cost and is not always required.
Two geared polycentric hinges are known to us in which insert elements may be added to effectively jam the gears and limit the extent of pivotal movement. One such geared hinge is used in a brace by Donjoy Inc. of Carlsbad, Calif., U.S.A. and the other is a plastic hinge made by Otto Bock of Duderstadt, West Germany.
Accordingly, an important aspect of this invention lies in providing a true bipivotal hinge in which the hinge arms may pivot independently in relation to each other and to a hinge body and in which a simple but highly effective system is provided for altering the hinge so that the extent of pivotal movement of the arms is selectively controlled. In such a system, a plurality of insert elements are provided, each insert element being capable of being readily attached to or removed from the hinge body for controlling the extent of pivotal movement of the respective hinge arms. Since the insert elements are constructed to limit pivotal movement at different selected angles, such insert elements may be interchanged so that any given hinge mechanism is tailored to the needs of a patient. As those needs change, the insert elements may be changed accordingly. Conversely, if the same brace is to be re-used with a different patient, the limits of pivotal movement may be easily modified by simply interchanging the insert element to meet the needs of the second patient.
Briefly, the bipivotal hinge system takes the form of a hinge body having a pair of side walls defining a space therebetween. Two hinge arms have adjacent end portions located in that space, the arms being pivotally connected to the side walls for independent flexion/extension with respect to the other arm. A plurality of insert elements are provided, each having a mounting portion and two integral stop portions. The mounting portions of all of the insert elements are of substantially the same size and shape but the stop portions of the respective elements are of different size and shape. Since the stop portions of the different insert elements are engagable with the arms at different angles of pivot for each of the plurality of insert elements, the extent of independent pivotal movement of the hinge arms may be selectively controlled simply by interchanging the insert elements in the hinge body. Connecting means are provided for removably securing any one of the insert elements in the hinge body with the stop portions thereof positioned for engagement with the adjacent end portions of the hinge arms for limiting the extent of independent pivotal movement of each of those arms.
In a preferred embodiment, each insert element is of generally T-shaped configuration, having a central stem that constitutes the mounting portion of the element and a pair of outwardly-projecting top members that constitute the stop portions of the element. The top members project outwardly in opposite directions with each top member having an abutment surface for engagement with one of the hinge arms. The angles of the abutment surfaces differ from one insert element to the next and may even, if desired, differ for the two abutment surfaces of a single insert element.
Other features, advantages, and objects of the invention will be apparent from the specification and drawings.